The present invention relates to vapor sensors, and more particularly to such sensors using optical elements.
The development of reversible devices--devices which can be reused--for detecting toxic gases such as ammonia and hydrazine, is currently an active area of research.
The first description of a device utilizing an organic film-coated optical waveguide for vapor detection was published in Nature, Vol. 257, p.666 in 1975 by Hardy, David, Kapany, and Unteilertner. These authors used the chemical reaction between cyanide ions and a picrate dye film coating on the surface of a light-guiding quartz rod to detect the presence of the cyanide ions. The chemical reaction between the cyanide ions and the coating changes the refractive index and absorption coefficient of the coating. The resulting chamber in light transmission through the rod is proportional to the concentration of the cyanide species. Subsequently, Hardy, David, Willson, and Ruffin described in Anayltical Letters Vol. 9, p. 389 (1976), a similar device incorporating a ninhydrin-coated quartz rod which could detect ammonia vapor concentrations of below 100 ppb. For both of these devices however, the dye reactions are chemically irreversible and hence the devices are of limited practical use.